Polyvinyl acetal resins are excellent in toughness, film formation properties, properties for dispersing inorganic or organic powder such as pigments therein, and adhesiveness to the coated surface. Therefore, they are suitably used in, for example, ceramic green sheets and conductive pastes used for constituting multilayer ceramic capacitors, ink, paints, baking enamels, and wash primers.
Particularly, multilayer ceramic capacitors are normally produced through the following steps.
First, ceramic material powder is added to a binder resin such as a polyvinyl butyral resin, and they are uniformly mixed to produce a slurry composition. The slurry composition is applied to a surface of abase subjected to releasing treatment in advance. The applied slurry composition is heated so that volatiles such as solvents therein are removed, and then peeled from the base to produce a ceramic green sheet. Then, a conductive paste containing ethyl cellulose, a polyvinyl butyral resin, or the like as a binder resin is applied to the obtained ceramic green sheet by screen printing. A plurality of such sheets are alternately laminated and thermocompressed to each other. The obtained lamination is degreased and fired to produce a ceramic fired body. On end faces of the ceramic fired body, external electrodes are sintered. In this manner, multilayer ceramic capacitors are produced.
Recent needs for downsized multilayer ceramic capacitors with higher capacity lead to studies to achieve further increase in the number of layers and further reduction in film thickness. In such multilayer ceramic capacitors, ceramic green sheets have become thinner and thinner. Along with this, ceramic powder to be used is required to have a smaller particle size.
A common method for dispersing ceramic powder and the like in a slurry composition, as disclosed in Patent Literature 1, comprises the following steps. An inorganic dispersion comprising an inorganic powder and an organic solvent is prepared. Separately, a resin solution comprising a binder resin dissolved therein is prepared. Then, the inorganic dispersion and the resin solution are mixed.
However, this method requires stirring of a liquid mixture for a long time to avoid insufficient dispersion of ceramic powder. Such stirring problematically consumes excessive energy and time.
Further, a method for ensuring the dispersibility of ceramic powder in the slurry composition include, as disclosed in Patent Literature 2, a method of adding a dispersant. However, in a case where the used dispersant has poor compatibility with the binder resin, this method may lower the dispersibility.
In producing a multilayer ceramic capacitor, a ceramic slurry composition produced may be stored for several days before application. In this case, if the long-term dispersion stability of the slurry is insufficient, a ceramic green sheet to be obtained has reduced strength and larger surface irregularities due to reduction in the dispersibility. This causes a problem of reduction in electric properties of a multilayer ceramic capacitor to be obtained.